inoculation, process of producing immunity that consists of introduction of the infectious agent into the body. Historically, inoculation involved introducing the infectious agent onto an abraded or absorptive skin surface. Following the development of vaccines, inoculation also came to include vaccination, which involves the introduction of a modified, weakened version of the infectious agent into the body, usually by means of injection but also orally or nasally. The term inoculation may also be applied more generally to refer to the introduction of a microorganism into a new environment—for example, the inoculation of bacteria into a culture medium.